Dispersants are substances that improve the flow characteristics of the cement slurry by breaking up cement agglomerates and freeing the water, thus giving slurries of lower viscosity and allowing desirable flow conditions to be obtained at lower pump pressures. V. S. Ramachandran, Concrete Admixtures Handbook: Properties, Science, and Technology, Noyes Publications (Second Edition, 1995). Superplasticizers such as sulfonated melamine formaldehyde condensate (SMF) and sulfonated naphthalene formaldehyde condensate (BNS) are commonly used as dispersants. However, these compounds require more than the desired amount of material to achieve a desired level of concrete workability or water reduction. In addition, these materials do not achieve full range (Type A to Type F) water reducing capability.
It is important that dispersants are used in concrete situations where strength and durability are involved, as dispersants are a necessary component in high strength and high durability concretes. Due to the use of low water amounts in the high performance concretes, sometimes high dispersant amounts are necessary to achieve workable concretes. High BNS levels can lead to undesirable retardation of set and may not provide the required workability retention over time.
It is desirable to provide a material that is several times more efficient as a cement or concrete dispersant than the traditional materials like BNS and SMF. Improving efficiency reduces the amount of material required to achieve a desired level of concrete workability or water reduction. With respect to the presently used dispersants, BNS and SMF, it is also desirable to improve slump retention while maintaining normal setting characteristics. Providing a dispersant with full range (Type A to F) water reducing capability is also a desirable characteristic.
According to German Patent Application No. 4,427,233, aspartic acid is produced by bringing (a) maleic anhydride, maleic acid, fumaric acid, and/or malic acid into contact with (b) ammonia and/or primary or secondary amines in a molar ratio of (a) to (b) of 1:0.1-1:3, possibly in the presence of co-condensable compounds. Components (a) and (b) are brought into contact with each other at temperatures of above 100.degree. C. and thermally condensed, and the polycondensates are then hydrolized, if desired. Components (a) and (b) are brought into contact with each other in the presence of condensation products of the reaction products of (a) and (b) and of powders which are inert under the polymerization conditions. Polymers which contain aspartic acid imide units in the backbone are thus formed.
Other methods of producing polyaspartic acid are disclosed in WO Publication No. 97/18249, Great Britain Patent No. 2307689, and Japanese Patent Application No. 5-321720. Japanese Patent Application No. 5-321720 discloses a hydraulic cement admixture for use as a dispersant, a water reduction agent, and a flowing agent. The effective components of this hydraulic cement admixture are polyaspartic acid and monomeric derivatives. A relatively high percentage of these additives is required for performance as dispersants.